1. Field of the Invention
The present invention relates to a rotating disc-type biological waste water treatment apparatus including one or more rotating disc assemblies arranged in tandem or in parallel and rotatively driven while their lower halves are immersed in waste water for its purification and more particularly novel rotating disc assemblies for use in the treatment apparatuses and a method of producing the rotating disc assemblies.
2. Description of the Prior Art
The rotating disc-type waste water treatment apparatuses for purifying waste water have been known, whose principle is based on the fact that the bacteria, microorganisms and algae propagated on the surfaces of rotating discs whose lower halves are immersed in the waste water take up and digest the nigrogen or phosphorus in waste water as nutrient. Various waste water treatment apparatuses of the aforenoted rotating type have been proposed. It is generally required for the treatment apparatus to provide great areas for attaching the microorganisms to improve its purification without increasing outer diameters of the discs and axial lengths. It is also required for the apparatus to be light weight, compact and durable for long years and to be driven by driving power as little as possible.
In some instances of the prior art, circular discs formed on their both surfaces with recesses and protrusions have been proposed for the purpose of increasing the surface areas to improve the purification. However, there has been tendency of such rotating discs to increase the driving power. In order to make the rotating discs light, attempts have been made to produce the discs of foamed polystyrene, waterproof plywood and the like. However, the discs made of these materials may be inferior in durability.